Cyclone separating devices can be used to separate dust and other dirt from airflow by virtue of the centrifugal force produced by a highly revolving flow in the cyclone barrel. In the prior art, two-leveled cyclone separating devices are adopted in a serial, so that big sized dust can be extracted from the dust laden air firstly through an upstream separating device, then small dust particles are eliminated through a downstream separating device, which finally attains the purpose of purifying the air.
However, an obvious disadvantage of the known art mentioned above is its bulky size, which causes great trouble to the device operator. Besides, the long gas passageway between the two cyclone separating devices results in a complicated manufacturing process, which means more components and a higher production cost.
In an intention to solve the above mentioned problems, the U.S. Pat. No. 4,373,228 came up with a vacuum cleaning appliance with the downstream separating device partially mounted inside the upstream separating device. However, new problems come up. On one hand, the cyclone separating device must be cylindrical in shape; also, the radial dimension of the whole device must be very large due to the insertion of the downstream separating device inside the upstream separating device. The CN 2004100049368.3 patent disclosed another separating device with the downstream separating device mounted at the outside of the upstream separating device. Such designed device lowers its height to some extent, but is still large in radial direction, and thus finds no application in many cases.